The value is stored internally in radians, but is converted to and
from a degrees string for access. Some example input formats are:
"155:19:23.2", "155 19 23.2", "155:19.387", "155.32311", "E155.32311",
"-204.67689", "W204.67689". As indicated, the sign of the longitude can
optionally be indicated using characters "E" and "W" in place of the
usual "" and "-". When converting the stored value to a string, the
format "[s]ddd:mm:ss.ss" is used, when "[s]" is "E" or "W" and the
numerical value is chosen to be less than 180 degrees.
AST A Library for Handling World Coordinate Systems in Astronomy